1. Field of the Invention:
The present invention relates to a mass flow sensor and more particularly to a mass flowmeter, for example, for use in determining an intake air flow for an internal combustion engine.
2. Description of the Prior Art:
In an electronically controlled fuel injection gasoline engine, a quantity of intake air flow into the engine is detected and a quantity of fuel to be injected is controlled with the aid of the detected intake air flow so as to obtain a desired air-fuel ratio.
The intake air varies much greatly in specific weight depending upon atmospheric pressure and temperature than the fuel, and, therefore, if the fuel is supplied to the engine only according to the measured volume flow of the intake air, an actual air-fuel ratio will deviate from a desired value to lower an output performance with undesirable exhaust gas composition.
In order to solve this problem, it has been suggested to correct the measured quantity of flow according to the atmospheric pressure and temperature to eliminate the errors of the quantity of flow. However, a provision of two compensation means make the device complicated and expensive.
An intake air flow sensor has been suggested which comprises an inclined plate for changing an area of a passage depending upon a quantity of the flow, whose inclined angles are measured by a potentiometer. Such a sensor may lack reliability and be inferior in accuracy because of many movable parts included in the sensor.